Despite a variety of available analgesics, treatment of chronic pain remains a large unmet medical need. Although some chronic pain conditions may be treated adequately by existing drugs, many patients fail to achieve adequate pain relief. This is especially the case for patients suffering from neuropathic pain due to trauma, disease, and/or neurotoxic anti-retroviral pain, which are often unresponsive to conventional analgesics. Furthermore, the chronic use of many analgesics is limited by side effects or by the development of tolerance. In 2010, analgesics accounted for sales of $22 Billion globally and $13 Billion in the US (1. I. Melnikova, Nat. Rev. Drug Discov. 9, 589 (2010); 2. C. Harstall, Pain Clinical Updates X, 1 (2003)). The highest selling analgesics were opiates, followed by non-steroidal anti-inflammatory drugs (NSAIDs), antiepileptics, antidepressants, and local anesthetics.
The N-type voltage-gated calcium channel (CaV2.2) is a nidus for neurotransmitter release and transmission of nociception. However, it has been reported that the use of CaV2.2 blockers in pain therapeutics is limited by side-effects resulting from inhibition of the physiological functions of CaV2.2 within the CNS. The N-type voltage-gated calcium channel (CaV2.2) has recently gained immense popularity as one of the key factors in the ascending pain pathway (see reviews by Zamponi and Snutch (1,2)). As such, it is believed herein that regulation of CaV2.2 expression and function is posed to have a major impact on the presentation of multiple pain states. Inhibition of CaV2.2 by synthetic conopeptides has been reported to provide analgesic relief in a variety of platforms (3-6). However, given the importance of CaV2.2 integrity in peripheral and central synapses, directly targeting channel function is reportedly complicated by a myriad of adverse side effects (7-9). The use of calcium channel peptides as decoys to disrupt binding of regulatory proteins has previously been demonstrated using the II-III cytoplasmic loop (14) and the alpha interaction domain (AID) of CaV2.2 (15). Intracellular injection of a peptide containing the II-III loop, containing the synprint interaction site, prevented association of the CaV2.2 with the synaptic core complex, reducing synaptic transmission (15). Peptides containing the AID domain of CaV2.2 prevented G-protein-mediated inhibition of channel function by disrupting binding of the Gβγ subunit to the channel (14). Alternatives for existing therapies are needed.
It has been discovered herein that disruption of collapsin response mediator protein 2 (CRMP2) and N-type voltage-gated calcium channel (CaV2.2) protein-protein interaction is anti-nociceptive for both inflammatory and neuropathic pain. Described herein are compounds and pharmaceutical compositions for treating pain. Also described herein are uses of the compounds and pharmaceutical compositions described herein for treating pain, and methods for treating pain using the compounds and pharmaceutical compositions described herein.
In one embodiment, peptide inhibitors of the CRMP2-CaV2.2 protein-protein interaction, based on and derived from CRMP2, such as CBD3, and related peptides are useful in treating inflammatory and neuropathic pain. Without being bound by theory, it is believed herein that such peptide inhibitors, by perturbing interactions with the neuromodulator CRMP2, contribute to suppression of neuronal hypersensitivity and nociception. It is appreciated herein that CRMP2 is a protein capable of binding to and enhancing CaV2.2 activity. Using a peptide tiling array, novel peptides were identified that bind CRMP2. Illustrative of such peptides include those within the first intracellular loop (CaV2.2[388-402] ‘L1’) and the carboxyl terminus (CaV1.2[2014-2028] ‘Ct-dis’), each of which bind CRMP2. Microscale thermophoresis demonstrates micromolar and nanomolar binding affinities between recombinant CRMP2 and synthetic L1 and Ct-dis peptides, respectively. Co-immunoprecipitation experiments show that CRMP2 association with CaV2.2 is inhibited such L1 and Ct-dis peptides. L1 and Ct-dis, rendered cell penetrant by fusion with carrier proteins, such as but not limited to the protein transduction domain of the HIV TAT protein, are evaluated in in vitro and in vivo experiments. Depolarization-induced calcium influx in dorsal root ganglion (DRG) neurons is inhibited by the peptides described herein. The Ct-dis peptides strongly inhibits depolarization-stimulated release of the neuropeptide transmitter calcitonin gene-related peptide (CGRP) in mouse DRG neurons. Similar results are obtained in DRGs from mice with a heterozygous mutation of Nf1 linked to neurofibromatosis type 1. Ct-dis peptide, illustratively administered intraperitoneally, exhibits antinociception in Zalcitabine (2′-3′-dideoxycytidine (ddC)) model of AIDS therapy-induced peripheral neuropathy.
Without being bound by theory, it is believed herein that targeting protein-protein interactions which regulate CaV2.2 may provide similar analgesic benefits as direct inhibition while avoiding complications associated with channel block. Described herein are peptides derived from channel domains demonstrated to coordinate CRMP2 that target the reciprocal interface of the interaction.
In another embodiment, described herein are 15 amino acid length peptides derived from the I-II cytoplasmic loop and the distal C-terminus of CaV2.2 and CaV1.2, respectively. The peptides effectively disrupt the interaction between CRMP2 and CaV2.2, reducing calcium influx. These channel regions are known to coordinate interactions between the channel and many other regulatory proteins. The I-II cytoplasmic loop contains interaction sites for CaVβ proteins (16) as well as Gβγ subunits (17). Additionally, the carboxyl terminus also contains interaction sites for Gβγ subunits (18). Calmodulin has also been shown to interact with this region (19-22). However, the illustrative 15 amino acid peptides described herein do not overlap with the binding sites for calmodulin or the Gβγ subunits (23,24), but there is partial overlap of the L1 peptide with the carboxyl terminal portion of the AID, which is responsible for binding CaVβ.
In another embodiment, the peptides described herein are useful in treating mechanical hyperalgesia associated with HIV retroviral treatment-induced neuropathy when administered systemically. For example, systemic administration of Ct-dis peptide transiently reverses mechanical hyperalgesia associated with HIV retroviral treatment-induced neuropathy.
In another embodiment, pharmaceutical compositions containing one or more of the compounds are also described herein. In one aspect, the compositions include a therapeutically effective amount of the one or more compounds for treating a patient with pain. It is to be understood that the compositions may include other component and/or ingredients, including, but not limited to, other therapeutically active compounds, and/or one or more carriers, diluents, excipients, and the like. In another embodiment, methods for using the compounds and pharmaceutical compositions for treating patients with pain are also described herein. In one aspect, the methods include the step of administering one or more of the compounds and/or compositions described herein to a patient with pain. In another aspect, the methods include administering a therapeutically effective amount of the one or more compounds and/or compositions described herein for treating patients with pain. In another embodiment, uses of the compounds and compositions in the manufacture of a medicament for treating patients with pain are also described herein. In one aspect, the medicaments include a therapeutically effective amount of the one or more compounds and/or compositions for treating a patient with pain.
It is to be understood herein that the compounds described herein may be used alone or in combination with other compounds useful for treating pain, including those compounds that may be therapeutically effective by the same or different modes of action. In addition, it is to be understood herein that the compounds described herein may be used in combination with other compounds that are administered to treat other symptoms of pain.